The invention relates to a light generator comprising a housing accommodating a light source and an optical system for directing the radiation to be generated by the light source.
Such light generators are known per se. They are used, inter alia, for general lighting purposes, for so-called sign and contour illumination, for signal illumination, such as in traffic lights or traffic-control systems, for example in road-marking systems for dynamically or statically controlling traffic flows. Such light generators are further used in projection illumination and in fiber-optical illumination.
A light generator of the type mentioned in the opening paragraph is known from U.S. Pat. No. 5,803,575. The known light engine is provided with a light source in the form of a high-pressure metal iodide lamp. The radiation generated by this lamp is directed via an optical system in the form of a reflector and a focusing lens to the end of a bundle of optical fibers.
A drawback of the known light generator is that the light source appears to emit much heat in the form of IR-radiation during operation. Besides, a relatively large quantity of UV-radiation is generated by the known lamp. As a result, it proved to be impossible to manufacture the reflector and the focusing lens from a synthetic resin. If these components of the optical system are made of a synthetic resin material, they are found to degrade under the influence of the UV-radiation and/or melt under the influence of the IR-radiation. Consequently, the reflector and the focusing lens are usually made of glass. In comparison with synthetic resin components, optical components of glass with the dimensional accuracy desired for this application are relatively expensive.
It is an object of the invention to provide a light generator in which the components of the optical system for directing the radiation to be generated by the light source can be made of a synthetic resin material.
These and other objects are achieved by means of a light generator comprising a housing accommodating a light source and an optical system for directing the radiation to be generated by the light source, wherein
the light source comprises at least one LED having a luminous flux which is at least 5 lm during operation of the light source,
and the light generator is provided with drive electronics for driving the LED.
The invention is based on the recognition that light-emitting diodes (LEDs) generate much less radiation heat and/or UV light than gas discharge lamps or halogen lamps. Consequently, LEDs are eminently suitable for use in light engines. For the desired applications, such as projection illumination and fiber-optical illumination, the luminous flux of the LEDs of the light generator should be sufficiently high, namely 5 lm or more. Since the LEDs of the light engine according to the invention can be chosen to be such that they emit little or no UV and/or IR-radiation, it is now possible to manufacture the optical system of the light generator from a synthetic resin material. In this respect, good results have been achieved with optical systems of poly[methylmethacrylate] (PMMA).
It is noted that, in principle, it is possible to manufacture unicolored light generators which are provided with a single LED. In practice, a substrate with a plurality of LEDs as the light source of the light generator will be employed in many cases. This applies, in particular, if the desired color of the light generator can be obtained only by mixing the colors of different types of LEDs.
Further advantages of the use of LEDs are the compactness of such light sources, a relatively very long service life, and the relatively low costs of energy and maintenance of a light engine comprising LEDs. The use of LEDs also has the advantage that dynamic lighting possibilities are obtained. If different types of LEDs are combined and/or LEDs of different color are used, colors can be mixed in the desired manner and color changes can be effected without the use of a so-called color wheel being necessary. The desired color effects are achieved by using suitable drive electronics. In addition, a suitable combination of LEDs enables white light to be obtained, whereby drive electronics enable a desired color temperature to be adjusted, which color temperature remains constant during operation of the light generator.
LED is preferably mounted on a metal-core printed circuit board. When the LED(s) is (are) provided on such a metal-core printed circuit board (MC-PCB), the heat generated by the LED or the LEDs can be readily dissipated via the PCB by means of heat conduction.
The housing can be is made of metal and provided with cooling fins, with the metal-core printed circuit board in contact with the metal housing via a heat-conducting connection. Such a heat-conducting connection is preferably realized by mounting the MC-PCB on a metal plate which is connected to the metal housing. In this embodiment, the heat generated in the LED or LEDs can be dissipated by (thermal) conduction via the MC-PCB and the metal plate to the housing and the cooling fins, whereafter heat-dissipation to the surroundings takes place. An advantage hereof resides in that forced air cooling to dissipate heat is not necessary.
The invention is characterized in that the metal-core printed circuit board is cooled by means of forced air cooling. In this embodiment, an air stream is generated in the housing, during operation of the light engine, for example by means of a fan incorporated in the housing, which air stream is directed, for example, towards the MC-PCB. In this case, the housing may be made of a synthetic resin. It is to be noted that it is also possible to combine the measure of forced air cooling and the measures of removing heat via heat conduction, as mentioned in the previous paragraph.
A favorable embodiment of the light generator in accordance with the invention is characterized in that
the light source comprises a plurality of LEDs,
and in that the optical system comprises a collimator lens which is composed of a plurality of sub-lenses, an optical axis of each of the sub-lenses coinciding with an optical axis of one of the LEDs.
By means of this optical construction, the light from a number of LEDs can be satisfactorily focused. The sub-lenses of the collimator lens are preferably interconnected. In practice, the collimator lens is embodied so as to be an optically transparent plate of a synthetic resin material (for example PMMA), wherein the separate sub-lenses (one lens for each LED) are provided by means of injection molding.
An alternative, favorable embodiment of the light engine in accordance with the invention is characterized in that
the light source comprises a plurality of LEDs,
in that the optical system comprises a plurality of collimating elements, each LED being associated with one collimating element, and an optical axis of each one of the LEDs coinciding with an optical axis of the associated collimating element.
This measure enables the LED and the associated collimating element to be considered as one integrated element, which combination can be advantageously used, in the manufacture of the light generator, as a building block for an assembly of LEDs with associated collimating elements. It is even more advantageous to use combinations of three LEDs with three associated collimating elements as an integrated module, wherein each collimating element has a hexagonal structure enabling the collimating elements to be readily interconnected.
The light engine in accordance with the invention is characterized in that parts of the collimating preferably exhibit total internal reflection. In this manner, the light originating from the LED is emitted in a single direction by the optical system. As a result, the light output of the LED in the predetermined, specific direction is increased. Preferably, collimating elements are used which exhibit a combination of (total) internal reflection and refraction.
The invention is characterized in that the surface of the collimating elements facing away from the LEDs is preferably curved. As a result of this curvature, the dimensions of the collimating element are reduced without a reduction in functionality. By virtue thereof, a saving in costs is achieved because less material is necessary. In this manner, a compact and relatively inexpensive light engine having a high efficiency is obtained, the optical system being designed in such a manner that more light is emitted by the light engine (the light emitted is generally launched into an optical fiber).
To simplify the construction of the light engine, preferably, the LEDs and the associated collimating elements are arranged in a hexagonal assembly. By virtue thereof, the compactness and efficiency of the light engine are increased.
In a preferred embodiment of the light engine, the optical system also comprises a focusing lens. Preferably, the focusing lens of the optical system is embodied so as to be a Fresnel lens. This contributes to the compactness of the light generator. Such a Fresnel lens is preferably made of a synthetic material, for example PMMA, wherein the desired optical Fresnel structure is obtained by means of injection molding.
Drive electronics of the light engine may comprise means for changing the luminous flux of the LED. By using this measure, it is possible to dim the luminous flux. It is to be noted that the drive electronics are generally incorporated in the housing. In principle, it is also possible to arrange the drive electronics outside the housing.
Another interesting embodiment of the light generator is characterized in that the light source comprises a plurality of LEDs, in that the light source comprises LEDs which generate radiation of different wavelengths,
and in that the drive electronics of the light generator comprise means for adjusting the ratio between the luminous fluxes of the LEDs.
This measure enables the color and the color temperature of the light emitted by the light generator to be changed. By using suitable drive electronics, it becomes also possible, to make, for example, while light of a constant color temperature.
These and other aspects of the invention will be apparent from and elucidated with reference to the embodiments described hereinafter.